1. Field of the Invention
The present invention relates to an auto white balance controlling method and an electronic camera, and more specifically to a controlling technique for auto white balance adjustment applied to a digital camera or a video camera that can record a motion picture.
2. Description of the Related Art
Electronic image capturing apparatuses such as a video camera have an auto white balance adjustment function for balancing colors within a screen. Japanese Patent Application Publication No. 6-351037 proposes a method for continuously performing auto white balance (AWB) processing while capturing a motion picture by using an image signal obtained from an imaging device. According to this, a stable continuous AWB is achieved by reducing an abrupt change in a gain by integrating an integral of a color signal obtained from a screen corresponding to a field in a television system by several screens in a direction of time.
For such a method, however, high throughput has been required for a central processing unit (CPU) included in a camera because the CPU has to concurrently perform multiple processings including auto-focus (AF) processing, automatic exposure control (AE) processing, image processing and memory recording in addition to the above-mentioned AWB processing while capturing a motion picture. This has contributed to a higher cost of the camera.
On the other hand, if AWB while a motion picture is captured is fixed (made constant) due to the limited performance of the CPU, white balance adjustment cannot keep up with a change in a scene, for example in the case of a scene captured with a camera moving from an indoor scene into an outdoor scene. This is disadvantageous for resulting in a picture with unbalanced color.